The present invention relates to a temperature measuring sensor and to a method of producing same, and specifically to a temperature measuring sensor comprising terminal areas allowing good contacting with lead wires.
In conventional approaches, there has been a tendency to reduce the size of, or to miniaturize, structural elements and electric circuits more and more, so that, for example, a plurality of structural elements are produced at a high density on a single wafer or substrate, said plurality of structural elements subsequently being diced for further use.
The advantage of these miniaturizations is that on the one hand, the space taken up by the structural elements may be reduced in other components, and, which is also essential, that a plurality of such structural elements may be produced within a single substrate, so that the resources useful for production are used in an increasingly optimum manner. A plurality of structural elements may now be obtained from one substrate, so that an increased yield may be obtained by utilizing the same amount of material, so that the overall cost of each structural element is reduced with regard to the substrate material used, in accordance with the space taken up by the structural element.
One problem encountered with these progressive miniaturizations is that as the temperature measuring sensor becomes smaller, the contact faces available for connecting the temperature measuring sensor become smaller accordingly. For example, with temperature measuring sensors miniaturized in this manner, the available contact face does not provide sufficient mechanical strength for connecting with lead wires or other pads, so that a reduced level of connecting reliability results, particularly when using lead wires.
A conventional structural element is described in more detail with reference to FIG. 2, which structural element is a sensor chip or temperature measuring sensor, for example, wherein the contact areas are located on a common surface. This structural element comprises an insulating substrate 100, for example a ceramic substrate. A top surface 102 of the ceramic substrate 100 has a metal layer 104, e.g. a platinum film, formed thereon. The sensor chip comprises a first contact area 106 as well as a second contact area 108, which have a structured platinum film 110 arranged therebetween, for example in a meandering shape. Contact reinforcements 112 and 114 of a conductive material are located on the contact faces 106 and 108, respectively. In the example, shown in FIG. 2, of a conventional temperature measuring sensor, the measuring film 110 is protected by a glaze coating 116 located between the contact reinforcements 112 and 114. As may be seen, the contact faces 112, 114 are quite small compared to the overall dimension of the element, and as the level of miniaturization of the overall element increases, here, too, the available contact face for connecting to lead wires or the like decreases, so that the above-mentioned problems associated with the quality of the terminal connection result.
One example for solving these problems is discussed in DE 103 58 282 A1, and shall be discussed below with reference to FIG. 3, the elements known from FIG. 2 being provided with the same reference numerals here. An insulating layer 118 is located on the glaze 116 and on the reinforcement 112 of the first contact 106, said insulating layer 118 essentially covering the entire exposed top surface of the sensor element shown in FIG. 1, except for some of the reinforcement 114 of the second contact face 108. The surface thus formed has a conductive layer 120 deposited thereon, which covers the insulating layer 118 as well as the exposed area of the contact reinforcement 114 of the second contact 108. In addition, the substrate 100 has a via 122 formed therein, for example by means of a hole filled with a conductive material. The via 122 extends from the first contact 106 on the first surface 102 to a second surface 124 of the substrate 100. This second surface 124 has a further electrically conductive layer 126 formed thereon, which essentially completely covers the bottom surface 124 of the substrate 100 and is in contact, via the via 122, with the first contact 106 of the sensor device.
Even though the solution shown in FIG. 3 does well at solving the above-mentioned problems concerning attachment of the lead wires (e.g. when the lead wires are soldered) in that relatively large faces are provided, it has turned out that in particular when welding the lead wires, a very high thermal load occurs which in the present arrangement may cause problems, e.g. cracks in the underlying glaze coating, despite the “relatively large faces”.
One has found that during attachment of the lead wires to the top contact face 120, for example by means of resistance welding, an impairment of the underlying glaze coating 118 may occur which is caused by the “thermal shock-wave”. The welding impulse generates a sudden heat wave which propagates downward across the contact face (metal) and proceeds, within fractions of a second, as far as the underlying insulating layer (glaze) as a short heat pulse. Due to this sudden heat pulse, which is not isotropic even within a plane, but is stronger in the central area and less intense toward the outside, the glaze coating is heated up suddenly and unevenly, as a result of which thermal tensions build up which may lead to cracks in the glaze coating.
In unfavorable cases, the platinum meandering web underlying the glaze coating may also be damaged by this, which could result in an interruption of the resistor trace and, thus, in the sensor failing.